1. Field of the Invention
The subject invention pertains to the art of slip ring and brush assemblies which are commonly used to provide a rotatable electrical coupling between circuits in systems or instruments and particularly to those slip ring and brush assemblies which are subjected to a significant vibratory environment.
2. Description of the Prior Art
Presently slip ring and brush assemblies are constructed to provide a force normal to the slip ring at the point of contact between the brush and the slip ring due to spring tension in the brush. In an environment where the slip ring and brush assembly are subjected to significant vibratory forces the slip ring tends to repetitively slide with respect to the brush at the point of contact. This sliding action can be produced as a result of rotational or translational displacements of the slip ring which are caused by the vibratory forces. The sliding action of the ring with respect to the brush enables friction polymers to form between the ring and brush at the point of contact thus producing electrical discontinuities.
Although the chemical and physical properties of the materials in the slip ring and brush assembly are factors in polymer formation and the quantity and nature of the chemical compounds which contaminate the atmosphere feed the process, the polymer formation cannot take place in the absence of relative sliding movement between the slip ring and the brush surfaces at the point of contact. Thus, polymer formation is likely to be most severe in those applications of slip ring and brush assemblies which are subject to significant vibratory environments.
Prior art devices were designed so that the spring force in the brushes which acted normal to the point of contact between the brush and slip ring assembly was sufficient to maintain the brush and slip ring in contact. However, in a high vibratory environment the slip ring can translate or rotate in a dithering motion with respect to the brushes. This relative motion occurs because the stiffness of the brushes in the tangential direction at the point of contact between the brush and slip ring is greater than the vibratory force in the tangential direction exerted on the slip ring. As a result the brush remains stationary while the slip ring is slid back and forth against the brush at the point of contact.
The polymer formations which are produced as a result of the relative sliding motion between the brush and slip ring at the point of contact are growths of hydrocarbons and other compounds that are produced from volatiles that are present in the environment around the point of contact. Certain materials used in the construction of slip rings and brushes are more catalytic than others and certain chemical compounds more readily provide nutrients that would serve as the source for the polymers, but one of the essential ingredients in polymer formation is motion. There has to be relative sliding motion between the surfaces and in prior art slip ring assemblies the relative motion is produced in a vibratory environment by the dithering displacement of the slip ring assembly with respect to the brushes.
The subject invention provides a combination brush and slip ring assembly which inhibits the formation of the friction polymers thereby reducing the occurrence of electrical discontinuities in a brush and slip ring assembly.